1. Field of the Invention
The present invention relates to a process for purifying an organometallic compound. More particularly, it relates to a process for removing a trace amount of oxygen-containing component contained in an organometallic compound which is used as a raw material in the field of compound semiconductors.
2. Description of the Related Art
Organometallic compounds are recently used as raw materials for forming a thin film of a compound semiconductor by metal organic chemical vapor deposition (referred to as "MOCVD" hereinafter).
The thin film is not only utilized as a light-emitting diode, a laser diode and a microwave element but also is starting to be utilized as an ultraspeed IC and a opto-electronic IC.
However, the organometallic compound contains an oxygen-containing component as an impurity, which is formed by the reaction of the organometallic compound with air or moisture inevitably mixed during preparation or handling processes of the organometallic compound.
When the organometallic compound containing such the oxygen-containing component as an impurity is subjected to the above MOCVD, oxygen atoms are incorporated in the thin layer of the semiconductor. As the result, its electric and optical characteristics are extremely deteriorated to cause problems, for example, that only a film having high resistivity or low luminescent efficiency is obtained, or that elements using the thin layer have a short life even if a film having satisfactory properties could be obtained.
A fractional distillation method usually adopted for removing an impurity, i.e. the oxygen-containing component, cannot reduce its content in the organometallic compound to below hundreds of ppm since the vapor pressure of the oxygen-containing component is similar to that of the organometallic compound.
Japanese Patent Kokai No. 67230/1990 proposes a process for purifying an organometallic compound containing an oxygen-containing component in which it is treated with a hydrogenated metal compound such as sodium hydride, lithium aluminum hydride, etc. in an amount of 0.1 to 50% by weight, based on the organometallic compound.
Japanese Patent Kokai No. 112991/1991 proposes a process for purifying an alkyl aluminum containing an oxygen-containing component in which it is treated with an aluminum halide such as aluminum bromide, aluminum iodide, etc.
However, since the hydrogenated metal compound or the aluminum halide mentioned above itself has high decomposition tendency by moisture, these processes have problems, for example, that their dealing should be strictly controlled for maintenance or control of the activities of the reagents, and that reproducibility of the effect is poor. Therefore, a process for purifying organometallic compounds which does not have such the problems and is industrially excellent is desired.